Advanced digital map computer systems and, in particular, digital map computer systems capable of displaying a texture mapped perspective view require a capability for generating three dimensional symbology. The data structure of the three dimensional symbology must be compatible with digital terrain transformation pipeline processing techniques. Known symbol generators are two-dimensional in nature and do not position the symbology in three dimensional world coordinate space. Also using known techniques, two dimensional graphic symbology can be overlaid onto a digital map display but not positioned in depth.
The present invention provides a method and apparatus for translating a generic three dimensional library position of symbolic icons into the three dimensional world coordinate system of the digital terrain as displayed on a digital map system. The polygon description of the symbol can then be transformed by the same perspective transformation circuitry utilized for the other polygons, including terrain polygons. The data structures of the stored library symbols may be tagged with attributes to vary the appearance of the rendered symbol. Each vertex of a polygon may have red, green and blue (RGB) color attributes as well as an alpha-transparency factor, or texture mapping address. These attributes allow for varying the individual polygon facets which comprise a total icon. The three dimensional rendering may be placed any where in world space resulting in proper perspective viewing.